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400
Democritus
Democritus was a Philosopher. Proposed that Matter is made of little pieces. He believed matter was built with little building blocks that made everything that the human eye can or cannot see. Without his ideas we could not define atomic theories. -
400
Aristotle
Aristotle, a Philosopher, believed that all elements are made of the four substances; earth, air, fire and water. He was influenced by Plato and other Philosophers. He believed that everything wasn't made of atoms and there was something more in matter. His ideas were believed until later scientists of the 1800 century changed it. -
John Dalton
John Dalton, a chemist, created the first atomic theory. He proposed the Behavior of Gases and how all gases could be liquified. He then stated that the pressure of a gas varies in direct proportion to its temperature. He created ratios and defined how compounds are made. Compouds have there own ratio and they cannot be changed. -
J.J. Thomson
J.J. Thomson, was physicist, discovered electrons and noticed that an atom can be divided. Also, he concluded atoms are made of positive cores and negatively charged particles within it. He created the Plum Pudding Model before the nucleus was discovered. This model showed that the electrons are surrounded by a "pudding" of positive charges to be equal to the negative charges. -
Robert Millikan
Robert Millikan began a series of experiments to determine the electric charge carried by a single electron. He got more precise results with his famous oil-drop experiment in which he replaced water (which tended to evaporate too quickly) with oil. . He had an exact value of Planck’s constant. He was a physicist -
Ernest Rutherford
Ernest Rutherford, a Physicist, began his work by studying the effect of x-rays on various materials. After the discovery of radioactivity, he studied the particles in uranium metal. He began to notice that alpha particles would not always behave in accordance to the plum pudding model of an atom when fired at a piece of gold foil. Some of the meterials went through the foil while others were deflected. These observations has been known as Rutherford's Gold Foil Experiment. -
Niels Bohr
Niels Bohr, a physicist, proposed that the model of an atom has similarities to the galaxy. Like how the Planets go around the Sun the electrons go around the Nucleus. He combined Rutherford's description of the nucleus and Planck's theory to prove his theory. He also discoverd the energy levels of the electrons. He soon earned a Nobel Prize for his discoveries. -
James Chadwick
James Chadwick, another physicist, proposed the idea of the neutron. He proved that there is a nutral part of the atom that was neither a negative charge nor a posetive charge. It is were the protons and the nuetrons are found. His works helped shape the atom and how the scientists look at it.
